Enable Gatling HTTPS support and path configuration

**Is your feature request related to a problem? Please describe.**

The Gatling performance tests do not run against an HTTPS endpoint. And it always uses the `/log/ingest` endpoint, but this is now configurable.

**Describe the solution you'd like**

Continue the current pattern of using Java system properties to configure these values.

* `-Dprotocol=https`
* `-Dpath=/my/path`

